Cervix position before AF

Laura • I am 34 and have a 2 & 3yr old. DH and I struggled with infertility for several years and had a successful IVF with DD.
I looked on the support page but thought I would ask you guys...AF is due in 4 days. I am 12 DPO and a BFN. I noticed today doing a check my cervix is higher and firm. I had very light brown spotting yesterday and today an increase in CM
​So my question is, does CM increase before AF and should the cervix be low before AF?